[0001] This invention relates to curable coating compositions comprising a binder containing aliphatically unsaturated C=C group(s), for example a polysiloxane and a compound or polymer containing an aliphatically unsaturated group, which compositions can be cured for example using a curing agent or by the action of a siccative or by UV. The coating compositions can be cured by a radical reaction i.e. a chemical reaction between radicals. Such radical reaction is for example initiated by UV.

[0002] An aliphatically unsaturated group also called an aliphatically unsaturated hydrocarbon group is typically a chemical group containing at least one C=C unsaturation. A C=C unsaturation is also called a carbon to carbon unsaturation. An aliphatically unsaturated group is typically a group containing non aromatic C=C unsaturation(s). A binder as defined herein is a compound or mixture of compounds able to bind and form a coating on a substrate. A binder as defined herein can be a precured macromolecule able to react to form a polymer coating. The binder as defined herein can alternatively be a system, for example a mixture of compounds, able to cure and form a coating after curing. A siloxane or polysiloxane or organopolysiloxane is a silicon containing compound containing repeating Si-O-Si bonds. A silane is a silicon containing compound which does not contain repeating Si-O-Si bonds. The curable coating composition is especially suitable for metallic or overcoated metallic substrates. In particular it relates to the use of an organopolysiloxane additive in such coating compositions.

[0003] Curable polysiloxane coating compositions having a binder comprising a compound or polymer (D) containing at least one primary or secondary amine group, a compound or polymer (B) containing at least one ethylenically unsaturated double bond activated by an adjacent electron-withdrawing group, and a polymer (A) containing at least two silicon- bonded alkoxy groups are known. A compound or oligomer or polymer or component is a compound which can be polymeric or non-polymeric.

[0004] Typically (D) contains at least one silicon-bonded alkoxy group in its molecule. The coating is capable of curing at ambient temperature and humidity both by hydrolysis and condensation of the Si-O-C bonds of the polyorganosiloxane (A) and of the silicon-bonded alkoxy group in (D) and by Michael-type addition reaction of the amine (D) with the activated ethylenically unsaturated double bonds of (B). (D) can for example be an aminoalkyl silane.

[0005] Such polysiloxane coating compositions have high gloss which is retained remarkably well on weathering and UV exposure. They are particularly suitable for coating substrates which are exposed to the weather, e.g. sunlight, for long periods before recoating. The coating compositions can for example be used as a finish coating on substrates such as metal like zinc or aluminium, stainless steel, galvanised steel, glass or plastic surfaces. These are used for buildings, steel structures, automobiles, aircraft and other vehicles. A finish coating or overcoat can be applied on a substrate bearing a primer coat previously deposited on the substrate.

[0006] A curable coating composition according to the invention having a binder comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule and a compound or polymer (B) containing at least one aliphatically unsaturated group, is characterised in that the binder also comprises an

organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups.

[0007] The coating composition of the invention is curable for example by reaction with a compound or polymer (D) containing at least one primary or secondary amine group. The compound or polymer (D) containing at least one primary or secondary amine group is preferably packaged separately from the coating composition of the invention as defined above to form a 2-pack coating composition in which the packages can be mixed a short time before the coating composition is coated on the substrate. The curable coating composition according to the invention is mixed with a compound or polymer (D) containing at least one primary or secondary amine group. The cured coating may have improved properties compared to a coating which does not contain the organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups. The aliphatically unsaturated hydrocarbon groups of the organopolysiloxane (C) can react with the amine curing agent (D) by a Michael-type reaction so that the organopolysiloxane (C) becomes bound into the cured coating.

[0008] The improved properties of the coating may be one or more of the following:

increased overcoating interval, increased surface hardness or scratch resistance

(measured for example by the Clemen test or by Pencil hardness test), increased weatherability, increased hydrophobicity, increased adhesion, easier application process (viscosity, drying time), higher solvent resistance, better slip, better visual appearance, increased abrasion resistance (measured for example by the ink rubber test) or other improved mechanical properties.

[0009] The invention thus includes the use of an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups in a curable coating composition comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer (B) containing at least one aliphatically unsaturated group, and a compound or polymer (D) containing at least one primary or secondary amine group.

[0010] The invention also includes a process for coating a substrate, characterised in that the substrate is coated with a coating composition comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer (B) containing at least one ethylenically unsaturated carboxylic ester group, an

organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups and a compound or polymer (D) containing at least one primary or secondary amine group.

[0011 ] The coating composition of the invention can alternatively be cured by ultraviolet (UV) radiation. Alternatively, when the binder is an alkyd resin, the coating composition can be cured by the action of a siccative (Cobalt based or similar) and oxygen from air.

[0012] The organopolysiloxane (A) is a material based on a Si-O-Si polymer chain and may comprise mono-functional, di-functional, tri-functional and/or tetra-functional siloxane units. It is preferred that the majority of siloxane units are di-functional units having the general formula RR'Si0 _2/2 wherein R and R' each independently denotes an organic component or a hydroxyl or hydrogen substituent. Preferably R and R' are selected from alkyl groups, alkenyl groups, aryl groups, alkyl-aryl groups or aryl-alkyl groups. More preferably a substantial part, most preferably a majority of the R substituents will be alkyl groups having from 1 to 12 carbon atoms, most preferably methyl or ethyl groups. The organopolysiloxane can for example be a polydiorganosiloxane such as

polydimethylsiloxane (PDMS). Such a polydiorganosiloxane can for example have terminal silicon-bonded alkoxy groups. The terminal groups of the organopolysiloxane can for example be dimethylmethoxysilyl groups, dimethylethoxysilyl groups, methyldimethoxysilyl groups, methyldiethoxysilyl groups, triethoxysilyl groups or trimethoxysilyl groups. The organopolysiloxane (A) can for example comprise 3 to 100 siloxane units, preferably 4 to 25 siloxane units.

[0013] Some of the R groups of the organopolysiloxane (A) can be alkyl groups bearing an alkoxysilyl moiety, for example a trialkoxysilyl moiety. An example of such an

organopolysiloxane is the dimethyl methyloctyl methyl(triethoxysilyl)propyl siloxane copolymer.

[0014] The organopolysiloxane (A) can be an organopolysiloxane comprising at least one of the following units: M unit (mono-functional), D unit (di-functional), T unit (tri-functional), Q unit (tetra-functional). A M unit has the formula R3Si01/2 wherein R is a substituent, preferably an organic substituent and each R can be the same or different on a single Si atom. A D unit has the formula R2Si02/2 wherein R is a substituent, preferably an organic substituent and each R can be the same or different on a single Si atom. A Q unit has the formula Si0 _4/2 . A T unit has the formula RSi0 _3/2 , wherein R is a substituent, preferably an organic substituent. Each substituent R can be selected for example from alkyl, aryl, alkenyl, acrylate, methacrylate and others. For example it can be an alkenyl group having 1 to 6 carbon atoms, for example a vinyl group or an hexenyl group. [0015] A branched organopolysiloxane typically contains at least one T unit and/or at least one Q unit. A linear organopolysiloxane typically contains D units and optionally M units.

[0016] Although it is preferred that the majority of siloxane units of the organopolysiloxane (A) are di-functional siloxane units other units such as tri-functional or tetra-functional units may also be present resulting in the polymer chain exhibiting a certain amount of branching. For example resinous organopolysiloxane materials may be used such as a condensation product of a partially hydrolysed trialkoxysilane. The organopolysiloxane (A) can alternatively be a resinous oligomeric alkyl silicate, for example the material sold under the trade mark DOW CORNING ® US/CF/2403 resin. Blends of such resinous

organopolysiloxane materials with an alkoxy-tipped linear polyorganosiloxane such as PDMS can be used.

[0017] The organopolysiloxane (A) is preferably present as at least 25% by weight of the binder of the curable coating composition, and may for example be present at from 40% up to 85% of the binder.

[0018] The aliphatically unsaturated group in the compound or polymer (B) is preferably activated by an adjacent electron-withdrawing group, for example a carboxyl group. The aliphatically unsaturated group can bean ethylenically unsaturated group. Most preferably it comprises an ethylenically unsaturated double bond, that is a -CH=CH- bond, activated by an adjacent electron-withdrawing group, particularly an ethylenically unsaturated carboxylic ester group such as an acrylate or methacrylate. Acrylate ester groups are preferred because they are more reactive in the Michael reaction than methacrylate groups, particularly at ambient temperature. Compounds or polymers (B) containing other olefinically unsaturated groups activated by an adjacent carboxyl group, for example containing a maleate or fumarate ester group, can also be used effectively.

[0019] The compound or polymer (B) preferably contains at least two aliphatically unsaturated groups, more preferably at least two aliphatically unsaturated groups each activated by an adjacent electron-withdrawing group. (B) can for example be an oligomer or polymer, for example of molecular weight at least 300 up to 5000, preferably up to 3000, containing at least two acrylate or methacrylate groups. The acrylate or methacrylate groups are preferably present in the oligomer or polymer as terminal groups.

[0020] One preferred type of oligomer or polymer (B) is a urethane acrylate. This can be formed for example by the reaction of an isocyanate-tipped prepolymer with a hydroxyalkyl acrylate or methacrylate such as hydroxyethyl acrylate. Alternatively, the oligomer or polymer (B) can be an epoxy resin acrylate or methacrylate, a polyether acrylate or methacrylate, a polyester acrylate, a melamine resin acrylate, a polyamide acrylate, or an acrylic polymer having pendent acrylate or methacrylate groups. [0021] An alternative oligomer or polymer (B) is a polyester oligomer containing maleate or fumarate ester units.

[0022] The compound or polymer (B) can alternatively be a drying alkyd resin. Alkyd resins are polyesters derived from polyols such as trimethylolpropane, glycerol, or pentaerythritol and a dicarboxylic acid or carboxylic acid anhydride such as phthalic anhydride or maleic anhydride modified by the addition of fatty acids. Drying alkyd resins include

polyunsaturated fatty acids such as linolenic acid or linoleic acid, or drying oils which comprise triglycerides of polyunsaturated fatty acids. Examples of drying oils include linseed (flax seed) oil, tung oil, poppy seed oil, perilla oil, and walnut oil.

[0023] The compound or polymer (B) can alternatively be an acrylate or methacrylate ester of a polyol, for example propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, trimethylolethane triacrylate, 1 ,6-hexanediol diacrylate, 1 ,4-butanediol diacrylate, pentaerythritol triacrylate and/or pentaerythritol tetraacrylate, and/or a corresponding dimethacrylate.

[0024] The component (B) can be a blend of a compound and a polymer, for example a blend of an acrylate or methacrylate ester of a polyol with an oligomer or polymer containing at least two acrylate or methacrylate groups.

[0025] The compound or polymer (B) is preferably present as at least 10% by weight of the binder of the curable coating composition and may be present at up to 40 or 50% by weight of the binder. An oligomer or polymer containing acrylate or methacrylate groups can for example be present at 15% up to 50% by weight of the binder.

[0026] The organopolysiloxane (C) can be an organopolysiloxane comprising at least one of the following units: M unit, D unit, T unit, Q unit. A M unit has the formula R3Si01 /2 wherein R is a substituent, preferably an organic substituent and each R can be the same or different on a single Si atom. A D unit has the formula R2Si02/2 wherein R is a substituent, preferably an organic substituent and each R can be the same or different on a single Si atom. A Q unit has the formula Si0 _4/2 . A T unit has the formula RSi0 _3/2 , wherein R is a substituent, preferably an organic substituent. Each substituent R can be selected for example from alkyl, aryl, alkenyl, acrylate, methacrylate and others. For example it can be an alkenyl group having 1 to 6 carbon atoms, for example a vinyl group or an hexenyl group.

[0027] The organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups can be a linear or branched organopolysiloxane. The aliphatically unsaturated hydrocarbon groups of organopolysiloxane (C) are preferably silicon-bonded alkenyl groups but can alternatively be alkynyl groups. Examples of alkenyl groups include vinyl, allyl, butenyl, pentenyl and hexenyl groups. Vinyl and hexenyl, particularly 5-hexenyl, groups are preferred. The aliphatically unsaturated hydrocarbon groups can be terminal groups on the organopolysiloxane and/or can be groups pendant on the siloxane polymer chain.

[0028] The organopolysiloxane (C) can for example be a branched organopolysiloxane containing at least two, preferably at least three aliphatically unsaturated hydrocarbon groups, particularly at least two, preferably at least three alkenyl groups. The branched organopolysiloxane (C) can for example comprise one or more Q units of the formula Si0 _4/2 and/or one or more T units of the formula RSi0 _3/2 , preferably up to 1000 D units of the formula R ₂ Si0 ₂ /2 and M units of the formula R ₃ SiOi _/2 , wherein R is a substituent. The substituents R are selected for example from alkyl, aryl and alkenyl groups having 1 to 6 carbon atoms, at least two, preferably at least three substituents R in the branched siloxane being alkenyl groups, for example vinyl groups or hexenyl groups, acrylate groups, methacrylate groups. Examples of suitable branched organopolysiloxanes include those described in EP-A-1070734, which describes branched organopolysiloxanes comprising one or more Q units of the formula Si0 _4/2 , from 15 to 995 D units of the formula R ₂ Si0 _2/2 and M units of the formula R ₃ SiOi _/2 . In particular EP-A-1070734 describes branched organopolysiloxanes comprising one or more Q units of the formula Si0 _4/2 , from 15 to 995 D units of the formula R ₂ Si0 _2/2 as defined above and M units of the formula R ^a R ^b ₂ Si0 _1/2, wherein the R ^a and R ^b substituents are selected from alkyl, aryl and alkenyl groups having 1 to 6 carbon atoms, at least three R ^a substituents in the branched siloxane being alkenyl groups. The branched organopolysiloxanes of EP-A-1070734 usually have their alkenyl groups in the M units, which can for example be dimethylvinylsilyl units. Each R ^b substituent can be an alkyl group for example, a methyl, ethyl, propyl, isopropyl, butyl, pentyl or hexyl group; preferred are methyl and ethyl groups, particularly methyl groups.

[0029] Branched organopolysiloxanes (C) such as those comprising one or more Q units of the formula Si0 _4/2 , from 15 to 995 D units of the formula R ₂ Si0 _2/2 and M units of the formula R ₃ SiOi _/2 can alternatively have some or all of their alkenyl groups in the D units, which can for example include methylvinylsiloxane or hexenylmethylsiloxane units. It may be preferred that alkenyl groups present in D units are hexenyl groups. The branched organopolysiloxane (C) can include both vinyl and hexenyl groups; it can for example contain at least two, preferably at least three, dimethylvinylsiloxy M units, with at least 1 molar % of the groups R in the D units of the formula R ₂ Si0 _2/2 being hexenyl groups.

[0030] The organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups can alternatively be a linear organopolysiloxane, for example a short chain (degree of polymerisation less than 100 siloxane units) polydimethylsiloxane having terminal dimethylvinylsiloxy units. A linear organopolysiloxane (C) can alternatively or additionally have pendant alkenyl groups, for example it can include methylvinylsiloxane or hexenylmethylsiloxane units. A linear organopolysiloxane (C) can for example contain two terminal dimethylvinylsiloxy units and also one or more pendant hexenyl groups.

[0031 ] The organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups is preferably present in the curable coating composition at 1 to 15% or even 30% or even 99.9% by weight of the binder on a dry weight basis, more preferably 2 to 7%. The total amount of organopolysiloxane (A) plus organopolysiloxane (C) in the binder composition is preferably at least 40 or 50% by weight up to 85% or 90%.

[0032] The curable coating composition of the invention comprising an organopolysiloxane

(A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer (B) containing at least one aliphatically unsaturated group, and an

organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups can for example be cured by reaction with a compound or polymer (D) containing at least one primary or secondary amine group. Thus according to one aspect of the invention a curable coating composition of the invention comprises an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer

(B) containing at least one aliphatically unsaturated group, an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups and a compound or polymer (D) containing at least one primary or secondary amine group.

[0033] The compound or polymer (D) containing at least one primary or secondary amine group is preferably an amino-functional alkoxysilane, for example an

aminoalkylalkoxysilane. Such an aminoalkylalkoxysilane can react in the presence of moisture with the silicon-bonded alkoxy groups of the organopolysiloxane (A) in a siloxane condensation reaction and also with the aliphatically unsaturated groups in the compound or polymer (B) and in the organopolysiloxane (C) by Michael-type addition. The

aminoalkylalkoxysilane thus acts as an effective curing or hardening agent for the coating composition.

[0034] The aminoalkylalkoxysilane (D) is more preferably a trialkoxysilane. The compound (D) containing at least one primary amine group can for example be 3- aminopropyltrimethoxysilane, 3-amino-2-methyl-propyltrimethoxysilane or 3- aminopropyltriethoxysilane, or can be a disilane such as bis(3-aminopropyl)- tetramethoxysilane. A disilane compound contains a Si-O-Si bond. A compound (D) containing at least one secondary amine group can for example be N-methyl-3- aminopropyltrimethoxysilane or N-phenyl-3-aminopropyltrimethoxysilane. A compound (D) containing a primary amine group and a secondary amine group can for example be N-(2- aminoethyl)-3-aminopropyltrimethoxysilane. The aminoalkylalkoxysilane (D) can alternatively be a dialkoxysilane or monoalkoxysilane. A compound (D) containing at least one primary amine group can for example be 3-aminopropylmethyldimethoxysilane or 3- aminopropylmethyldimethoxysilane.

[0035] The amine group of the amino-functional compound or polymer (D) can be present in blocked form, for example as a ketimine, to extend pot life, if this is desired.

[0036] The organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups can be used in the curable coating composition together with a reactive alkoxysilane to form a coating composition providing excellent flexibility and hardness of the cured coating film. A preferred reactive alkoxysilane is an acrylate- functional alkoxysilane such as 3-acryloxymethyltrimethoxysilane or 3- acryloxypropyltrimethoxysilane. The organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups can if desired be mixed with an acrylate- functional alkoxysilane to form an additive package for improving the properties of a curable coating composition while maintaining the flexibility, hardness and scratch resistance of the cured coating. Alternatively the amino-functional curing agent (D) can include an aminoalkyltrialkoxysilane having an increased number of organic functional groups, for example a diamine such as aminoethyl aminopropyl trimethoxy silane or an aminoalkyltrialkoxysilane containing a group having carbon to carbon unsaturation such as 2-(N'-vinylbenzyl)aminoethyl-3-aminopropyltrimethoxysilane.

[0037] The molar ratio of amino groups of the amino-functional compound or polymer (D) to the total aliphatically unsaturated double bonds present in the compound or polymer (B) and the organopolysiloxane (C) of the coating composition is usually in the range 1 :10 to 10:1 , preferably at least 1 :2 up to 3:1 or 5:1 molar.

[0038] The curable coating composition of the invention comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer (B) containing at least one aliphatically unsaturated group, and an

organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups can alternatively be cured by UV radiation or initiated by oxygen from air with the help of a siccative.

[0039] When using a compound or polymer (D) containing at least one primary or secondary amine group as curing agent, the compound or polymer (D) is preferably packaged separately from the organopolysiloxane (A), the aliphatically unsaturated compound or polymer (B) and the organopolysiloxane (C) to form a 2-pack coating composition. The two packages of the coating composition can be mixed a short time before the coating composition is coated on the substrate, for example a short time before the coating is applied by brush, spray or roller. The separately packaged components can alternatively be applied by twin-feed spray. [0040] The coating compositions of the invention usually contain one or more pigments, and can contain other ingredients such as a siloxane condensation catalyst, for example a titanium alkoxide or an organotin compound, a thickening agent, a plasticiser, a pigment dispersant, a stabiliser, a flow aid or a solvent.

[0041] When using a compound or polymer (D) containing at least one primary or secondary amine group as curing agent, coatings of the composition of this invention are usually capable of curing at ambient temperatures of for example 5 to 30 ⁵ C. Coatings can be cured at elevated temperatures, for example in the range 30 to 130 ⁵ C, if heat curing is practical and is desired. Atmospheric moisture generally provides sufficient moisture for hydrolysis and reaction of the silicon-bonded alkoxy groups of organopolysiloxane (A) and an aminoalkylalkoxysilane curing agent (D) if present.

[0042] The coating composition of the invention can be applied as a primer coat or as a top coat on a substrate. The coating compositions of the invention containing the

organopolysiloxane (C) having at least two aliphatically unsaturated hydrocarbon groups provide coatings which may have improved properties.

[0043] Coatings formed from the coating compositions of the invention retain the high gloss, flexibility, hardness, scratch resistance and long term resistance to weathering and UV exposure.

[0044] The invention provides a curable coating composition, the composition containing a binder comprising

- an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule and optionally a compound or polymer (B) containing at least one aliphatically unsaturated C=C group provided that the binder contains at least one aliphatically unsaturated C=C group or

- a binder curable by radical reaction the binder containing an organopolysiloxane or a silane with at least one acrylate or methacrylate group or

- an alkyd binder containing at least one aliphatically unsaturated C=C group,

characterised in that the composition also comprises an organopolysiloxane (C) containing at least two aliphatically unsaturated C=C groups.

[0045] The invention provides a curable coating composition wherein the structure of the organopolysiloxane (C) is of the type MD and/or MDQ where in M or/and in D some of the R groups contain aliphatically unsaturated C=C groups. An MD structure contains M and D units without any T and without any Q units. An MDQ structure is a structure containing M, D and Q units without any T units.

[0046] The invention provides a curable coating composition wherein the structure of the organopolysiloxane is of the type MDTQ where in M or/and in D or/and in T some of the R groups contain aliphatically unsaturated C=C groups. An MDTQ structure contains together M, D, T and Q units.

[0047] The invention provides a curable coating composition wherein the aliphatically unsaturated hydrocarbon groups of organopolysiloxane (C) are silicon-bonded alkenyl groups.

[0048] The invention provides a curable coating composition wherein the aliphatically unsaturated hydrocarbon groups of organopolysiloxane (C) comprise vinyl groups.

[0049] The invention provides a curable coating composition wherein the aliphatically unsaturated hydrocarbon groups of organopolysiloxane (C) comprise hexenyl groups and/or acrylate groups and/or methacrylate groups.

[0050] The invention provides a curable coating composition wherein the

organopolysiloxane (C) is a branched organopolysiloxane containing at least two, preferably at least three aliphatically unsaturated hydrocarbon groups.

[0051] The invention provides a curable coating composition wherein the branched organopolysiloxane (C) comprises one or more Q units of the formula Si04/2, from 1 to

1000, preferably from 15 to 995 D units of the formula R2Si02/2 and M units of the formula R3Si01 /2, wherein the substituents R are selected from alkyl, aryl and alkenyl groups having 1 to 6 carbon atoms, at least two, preferably at least three substituents R in the branched siloxane being alkenyl groups.

[0052] The invention provides a curable coating composition wherein the branched organopolysiloxane (C) comprises one or more Q units of the formula Si04/2, from 1 to 1000, preferably from 15 to 995 D units of the formula R2Si02/2 as defined in Claim 6 and M units of the formula RaRb2Si01/2, wherein the Ra and Rb substituents are selected from alkyl and alkenyl groups having 1 to 6 carbon atoms, at least two, preferably at least three Ra substituents in the branched siloxane being alkenyl groups.

[0053] The invention provides a curable coating composition wherein at least 1 molar % of the groups R in the D units of the formula R2Si02/2 are alkenyl groups.

[0054] The invention provides a curable coating composition wherein the branched organopolysiloxane (C) comprises at least two, preferably at least three dimethylvinylsiloxy M units and at least 1 molar % of the groups R in the D units of the formula R2Si02/2 are hexenyl groups.

[0055] The invention provides a curable coating composition wherein the

organopolysiloxane (C) is present at 1 to 15% by weight of the binder on a dry weight basis.

[0056] The invention provides a curable coating composition wherein the compound or polymer (B) contains at least one ethylenically unsaturated carboxylic ester group. The invention provides a curable coating composition wherein the compound or polymer (B) comprises a drying alkyd resin.

[0057] The invention provides a curable coating composition further comprising as curing agent a compound or polymer (D) containing at least one primary or secondary amine group.

[0058] The invention provides a curable coating composition wherein the compound (D) containing at least one primary or secondary amine group is an aminoalkylalkoxysilane.

[0059] The invention provides the use of an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups in a curable coating composition having a binder comprising

- an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule and optionally a compound or polymer (B) containing at least one aliphatically unsaturated C=C group provided that the binder contains at least one aliphatically unsaturated C=C group or

- a binder curable by radical reaction the binder containing an organopolysiloxane or a silane with at least one acrylate or methacrylate group or

- an alkyd binder containing at least one aliphatically unsaturated C=C group,

characterised in that the composition also comprises an organopolysiloxane (C) containing at least two aliphatically unsaturated C=C groups.

[0060] The invention provides a process for coating a substrate, characterised in that the substrate is coated with a coating composition as defined above.

[0061 ] The invention provides an additive composition for a curable coating composition comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer (B) containing at least one aliphatically unsaturated group, and a compound or polymer (D) containing at least one primary or secondary amine group, said additive composition comprising an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups and an acrylate-functional alkoxysilane.

[0062] The invention provides a curable coating composition having a binder comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule and a compound or polymer (B) containing at least one aliphatically unsaturated group, characterised in that the binder also comprises an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups.

[0063] The invention provides an additive composition for a curable coating composition comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer (B) containing at least one aliphatically unsaturated group, and a compound or polymer (D) containing at least one primary or secondary amine group, said additive composition comprising an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups and an acrylate-functional alkoxysilane.

[0064] The invention provides the use of an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups in a curable coating composition comprising an organopolysiloxane (A) containing at least two silicon-bonded alkoxy groups per molecule, a compound or polymer (B) containing at least one aliphatically unsaturated group, and a compound or polymer (D) containing at least one primary or secondary amine group.

[0065] The invention provides the use of an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups in a curable coating composition comprising a binder curable by radical reaction the binder containing an organopolysiloxane or a silane with at least one acrylate or methacrylate group.

[0066] The invention provides the use of an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups in a curable coating composition comprising an alkyd binder containing at least one aliphatically unsaturated C=C group.

Examples

[0067] The invention is illustrated by the following Examples, in which parts and

percentages are by weight. In the Examples, coatings were evaluated by the following procedure:

[0068] Q-Panel' steel test panels were coated with a commercial primer and were allowed to dry in ambient temperature air for 7 days. The Dry Film Thickness is 100-150μηι.

[0069] The primer coat was overcoated with a 50μηι layer (dry film thickness) of a coating according to the invention and the coated panels were allowed to dry in ambient temperature air for 7 days. The coating according to the invention was a 2-pack paint modified by the addition of an organopolysiloxane (C) containing at least two aliphatically unsaturated hydrocarbon groups to the main package of paint. The paint is believed to comprise a curable coating composition. The main package (part A) is believed to be a pigmented coating composition comprising 25-50% of a silicone resin having

dimethylsiloxane units, methoxy groups and phenyl groups and silicon-bonded alkoxy groups, 10-25% acrylate-functional urethane oligomer, 10-25% 1 ,6-hexanediol diacrylate and 13-55% pigments. The curing agent package (part B) is believed to comprise a primary aminoalkyltrialkoxysilane.

[0070] Test panels overcoated with unmodified paint were also tested by the same process.

Examples 1 to 4

[0071] In each of these Examples, 5% of a trimethylsilyl, vinyldimethylsilyl-terminated poly(dimethylsiloxane-silicate) copolymer prepared by the process of EP-A-1070734 was added to part A of the paint described above. The trimethylsilyl, vinyldimethylsilyl- terminated poly(dimethylsiloxane-silicate) copolymers added in each Example are characterised as follows:

Example 1 - viscosity 250 cSt, weight average molecular weight Mw = 13000 and vinyl group content 1 .2 weight%

Example 2 - viscosity 80 cSt and vinyl group content 1 .13 weight%

Example 3 - viscosity 420 cSt and vinyl group content 0.95 weight%

Example 4 - viscosity 700 cSt and vinyl group content 0.40 weight%

Test results are shown in Table 1 below.

[0072] The Clemen hardness test is done to measure the scratch resistance of the surface of a coating. The test was conducted with an "Elcometer 3000 Motorised Clemen"

K0003000M003 (SN300012040007) tester. The sample is hold down with a clamp in the equipment. A load of defined weight is put on the sample and one observes which weight is needed to leave a trace on the coating.

Table 1

[0073] An unmodified paint resisted without trace on the coating up to a load of 800g while a paint as of examples 1 -4 containing the additive of the invention resists up to a load of at least 1000g.

[0074] The hardness of the surface as assessed by the Clemen test was thus improved.

Example 5

[0075] A commercial UV curable composition containing a silane acrylate binder was modified by inclusion of 5% of a trimethylsilyl, vinyldimethylsilyl-terminated

poly(dimethylsiloxane-silicate) copolymer prepared by the process of EP-A-1070734. The composition was applied on untreated aluminium panels. The trimethylsilyl,

vinyldimethylsilyl-terminated poly(dimethylsiloxane-silicate) copolymer added is

characterised as follows:

Example 5 - viscosity 250 cSt, weight average molecular weight Mw = 13000 and vinyl group content 1 .2 weight%.

[0076] In the following description, the terms "coating" and "film" are used to designate the same object i.e. a layer of paint applied on the surface of a substrate. [0077] The cross cut test is a test to measure the resistance of paints and coatings from substrates. A lattice pattern is made in the coating with a cross cut tool. Two passes are made, the second pass being perpendicular to the first. The cut is brushed in diagonal direction. A tape is applied on the grid, pressed and removed. The grid area is then observed. KO means the coating is fully destroyed. GtO means the best result (ISO2409).

[0078] The MEK test is a test to measure the solvent resistance of a coating. The surface of the coating is rubbed with cloth soaked with MEK (methyl ethyl ketone) until failure or breakthrough of the film occurs. Methyl Ethyl Ketone is rubbed across the surface of the part with a cloth (100 double rubs). The rubs are counted as a double rub (one rub forward and one rub backward constitutes a double rub). The higher the number, the better the solvent resistance of the coating is.

[0079] The slip test is a haptic test to evaluate the sensory touch of a film. A finger is applied on the film and the feeling is subjectively estimated by the operator. ++ means the feeling is very good.

[0080] The pencil hardness test is a test to evaluate the hardness of a film. A pencil of defined hardness is applied to the film. The pencils are classified from 6B (the softer) to 6H (the hardest): 6B 5B 4B 3B 2B B HB F H 2H 3H 4H 5H 6H. The pencil hardness of the film is the hardness of the hardest pencil that does not mark the film.

[0081] The ink rubber test also called ink rub test is a test to evaluate the abrasion resistance of a film. Sand paper is applied back and forth to a film sample by an ink rubber tester equipment. The number of strokes is programmed in the equipment. The tester stops automatically when the preset number of strokes is achieved. The samples are then evaluated visually for print degradation and ink transfer.

[0082] The water contact angle is measured with a VCA Optima equipment from AST Products, Inc S/N Optima 10200221019. A drop of water is applied on the film with the syringe incorporated into the equipment. The equipment calculates the contact angle which is the angle between the tangent to the drop at the point of contact and the solid surface of the film. This permits to evaluate the hydrophobic/hydrophilic nature of the film. A high contact angle is linked to a hydrophobic film while a low contact angle will be linked to a more hydrophilic film.

[0083] The pendulum Koenig test is a test to evaluate the hardness of a film. A Koenig tester equipment from Sheen Instruments S969320 707KP is used. The damping time of an oscillating pendulum is measured. The pendulum is oscillating between 3 and 6 degrees. The time (in seconds) taken for the pendulum to decrease from 6 to 3 degrees is measured.

[0084] The results are shown in the below table:

^* the product is dedicated to be applied at 5 μηι. Higher thicknesses are problematic because of high stress leading to weak mechanical properties of the film .